I know how paid per click and paid traffic works from buyer perspective. But does anyone know how people get the traffic to send in the first place? I mean do they just simply get a better price and resell it to us or do they actually know a way to get the traffic to send us?

I am not aware of such networks, what you are trying to achieve is arbitrage traffic. You can always lookout for such providers on Linkedin groups. I see a lot of advertising professionals active on that network.